Placenta and Fetal Membranes Amnion Epiblast Extraembryonic Mesoderm Yolk Sac Hypoblast Extraembryonic Mesoderm Allantois Embryonic Hindgut Chorion Trophoblasts ID: 353066
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Slide1
Embryonic Membranes and the PlacentaSlide2Slide3
Placenta and Fetal MembranesAmnion -
Epiblast
/
Extraembryonic
Mesoderm
Yolk Sac - Hypoblast /
Extraembryonic
Mesoderm
Allantois
- Embryonic Hindgut
Chorion
-
Trophoblasts
/
Extraembryonic
Mesoderm
Placenta -
Chorion
/ Maternal
DeciduaSlide4Slide5
AmnionAmnionic
membrane is two cell layers
As
the amnion enlarges it encompasses the embryo
Amnion forms the epithelial layer of the umbilical cord
With embryo growth the amnion obliterates the
chorionic cavity
Amnionic
sac is fluid filled called
amnionic
fluid: the
embryo is bathed in the fluidSlide6
Extraembryonic Tissues
9
days
8 days
14days
9 daysSlide7Slide8Slide9Slide10
AmnionSlide11
Amniotic FluidUp to week 20 - fluid is similar to fetal serum (
keratinization
)
After 20 weeks – Contribution from urine, maternal serum filtered
thru endothelium of nearby vessels, filtration from fetal
vessels in cord
Near birth - can contain fetal feces called
meconium
Near birth –
amnionic
fluid (500-1000 ml) exchanges every 3 hrs
1) across the amnion – exchange with maternal fluids.
2) fetal swallowing (20 ml/hour) – to gut – adsorption by
fetus – out the umbilical cord to placenta.
Hydraminos
– Excess fluid (>2000 ml), esophageal
atresia
Oligohydramnios – Insufficient fluid (<500 ml), renal agenesisSlide12
Amnion FunctionMechanical protection: hydrostatic pressure
Allows free movement - which aids in neuromuscular
development
Antibacterial
Allow for fetal growth
Protection from adhesionsSlide13
Yolk SacHypoblast - the primary yolk sac or
Heuser's
membrane.
Day 12 - Second wave of cell migration - forms definitive yolk sac
Early
nutrition (2-3 weeks) for the embryo - later shrinking
Derivatives:
Primordial
germ cells
The early gut, epithelium of the respiratory and
digestive tractsSlide14Slide15
Allantois
Endodermal
origin – caudal
outpocketing
of the yolk sac
Involved
in early
hematopoiesis
The
allantois
blood vessels - artery and vein
– becomes the
umbilical vessels
Remnants of
Allantois
becomes the urachus ligament that connects the belly button to the bladderSlide16
ChorionChorionic
cavity (
extraembryonic
coelom
)- lined
with
extraembryonic
mesoderm
The
Chorion
/ maternal
endometrium
forms the placenta
Chorion forms stem
villiSlide17
Stem VilliSlide18
Stem Villi
Chorionic
Plate – Stem
villi
extends from this tissue
Primary stem
villi
(day 11-13) - finger-like protrusions
into
endometrium
–
Secondary stem
villi
(day 16) -
extraembryonic
mesoderm invasion into villi core.
Tertiary stem villus (21 day) - extraembryonic vessels chorionic arteries and veins derived from
extraembryonic mesoderm.Slide19
Stem Villi
Cytotrophoblastic
shell
– surrounds embryo; direct
contact with
maternal
decidual
cells
Anchoring
Villi
– give off
cytotrophoblastic
extensions -
anchoring because they represent the real
maternal embryo linkFloating Villi – branches off anchoring
villi – dangles freely in maternal bloodSlide20
Making the PlacentaBy 8 weeks - chorionic stem
villi
over the entire surface of
the chorionic sac
Those
villi
increase in size
and more
villi
form.
The
villi
continue to enlarge during most of gestation.
Endometrial
vessels - spiral arteries and endometrial
veins formSlide21Slide22
PlacentaSlide23
Placental Blood FlowSlide24
Placental AnatomySlide25
Umbilical Cord
One
umbilical vein
,
Two umbilical
arteries
Wharton’s jelly –
connective tissue
surrounding vessels
Allantois
Yolk Stalk (
vitelline
duct) Slide26Slide27
Placenta as an Endocrine OrganHuman
Chorionic
Gonadotropin
– Corpus
Luteum
(declines after
8 weeks
)
Progesterone
– High levels by the end of first trimester
Estrogen
– Synthesis involves enzymatic activity of fetal
adrenal gland
and liver
Chorionic
Somatomammotropin – Human Placental Lactogen – similar
to GH (growth, lactation, lipid and carbohydrate metabolism)Placental Growth Hormone – similar to GH – Replaces
maternal GH by 15 wks – enhances blood glucose levelsSlide28Slide29
Should we look at a real one?